Hammer, Caleb2025-03-212025-03-212024-12https://hdl.handle.net/11299/270538University of Minnesota M.S. thesis. December 2024. Major: Land and Atmospheric Science. Advisor: Timothy Griffis. 1 computer file (PDF); viii, 79 pages.Dicamba herbicides are a critical tool for managing herbicide-resistant weeds, but their high volatility and potential for off-target movement have raised significant concerns about unintended damage to non-target crops and ecosystems. Despite reformulations aimed at reducing volatility, the persistence of dicamba-related drift continues to challenge growers and regulators. This research aimed to address these challenges using a measurement and modeling approach. The objectives of the research were to: 1) quantify dicamba concentrations in the atmosphere downwind of application sites; 2) measure dicamba loss and off-site transport using atmospheric sampling and Lagrangian transport modeling; 3) assess meteorological influences on dicamba volatilization and drift; 4) employ Geographic Information Systems (GIS) to analyze spatial and meteorological factors driving dicamba’s off-target movement; and 5) develop a risk-rating scale to guide counties in Minnesota on dicamba application risks.Field experiments conducted over multiple growing seasons combined air sampling with backward and forward Lagrangian stochastic models to estimate dicamba emissions and downwind transport. Results revealed that dicamba volatilization persisted for several days post-application, with peak emissions occurring within the first 24 hours. High temperatures, stable atmospheric conditions, and low wind speeds were identified as significant drivers of off-target movement, challenging the effectiveness of current label requirements and application guidelines. Geospatial analysis of dicamba damage across Minnesota from 2018 to 2022 highlighted southern and western counties as high-risk areas, driven by local meteorological conditions and soybean density. The analysis further identified critical meteorological thresholds, such as atmospheric stability, wind speed, and temperature, that exacerbate dicamba drift. By integrating experimental data with spatial and statistical analyses, this work provides a comprehensive evaluation of dicamba volatility and its impact on non-target crops. The findings emphasize the limitations of existing regulatory frameworks and underscore the need for stricter application guidelines that account for post-application volatilization and regional variability in risk. This work offers actionable insights for improving herbicide application practices, guiding regulatory strategies, and mitigating the environmental impact of dicamba in agricultural systems.enBiometeorologyMicrometeorologyThesis or Dissertation